Dust Ingestion Rates

There is considerable uncertainty surrounding dust ingestion rates, with those used derived from a very small number of studies using primary data collection (see 

---

Mean dust ingestion rates assumed to be 20mg/day (adults), 50mg/day (toddlers). 

Elucidate dust ingestion rates better, including how they vary with the dust loading in a microenvironment. 

EPA (2005b). Summary Report of the EPA Colloquium on Soil/dust Ingestion Rates and Mouthing Behavior for Children and Adults. EPA contract No. EP-C-04-027. National Center for Environmental Assessment, US Environmental Protection Agency, Washington, D.C. Accessed at http //cfpub.epa. gov/ncea/cfm/recordisplay.cfm deid=146585. 

More traditional approaches have calculated exposure doses from a particular medium via a specific route (ATSDR, 1992). Such exposure doses can then be compared with a reference value derived for the same substance via the same route of exposure. Usual assumptions are ingestion rates of 100 mg dust/day and 200 mg soil/day, child body weight of 15 kg, and continuous exposure scenarios. This approach assumes a threshold for the effects of lead and does not reflect the fullest possible use of the wealth of human data on PbB levels. 

Exposure routes would be ingestion and inhalation of dust. Even so, the dose rates that would be received by these pathways are very low (Murray and Avogadro 1979). 

Death. Occupational exposure of humans to 2,4-DNP has resulted in death (Gisclard and Woodward 1946 Perkins 1919). This exposure included airborne vapor, mists, dust, and direct dermal contact with the solid form of 2,4-DNP, indicating that exposure probably occurred via inhalation, dermal, and possibly oral routes. Death from occupational exposure to 2,4-DNP appeared to occur at a greater rate in workers having alcoholism or liver or kidney disease (Perkins 1919). Case studies reported death in humans ingesting 2,4-DNP and its sodium salt (doses expressed here as mg/kg... 

Occupational studies indicate that humans absorb elemental selenium dusts and other selenium compounds, but quantitative inhalation toxicokinetic studies in humans have not been done. Studies in dogs and rats indicate that following inhalation exposure, the rate and extent of absorption vary with the chemical form of selenium. Studies in humans and experimental animals indicate that, when ingested, several selenium compounds including selenite, selenate, and selenomethionine are readily absorbed, often to greater than 80% of the administered dose. Although a study of humans did not detect evidence of dermal absorption of selenomethionine, one study of mice indicates selenomethionine can be absorbed dermally. There is little or no information available on the absorption of selenium sulfides, but selenium disulfides are not believed to be absorbed through intact skin. 

---